From the start, Hour of Code had boosts from friends in high places. It was on the front page of both Google.com and Apple.com this week, and U.S. President Barack Obama even made a promo video. Code.org’s efforts apparently drove so much traffic to Khan Academy that the non-profit educational web site went down.

But the single biggest referrer to Code.org this week was individual teachers and schools who used the programs in their classrooms, according to Hadi Partovi, who co-founded the organization with his brother Ali Partovi. The two are repeat tech entrepreneurs and angel investors and have raised tens of millions of dollars to help increase the dismayingly low percentage of computer science classes in U.S. schools.

“I had hoped we could get one million students to do it and we were pleasantly surprised when 4.5 million signed up in advance,” Hadi Partovi wrote in an email to AllThingsD. “We’re now going to end the week with over 15 million, which is insane. That means every other school family in the U.S. has a child that has done the Hour of Code. I’m not aware of any technology or service that has spread so quickly, and this is computer programming.”

The 15 million number (it’s currently just shy of that) also doesn’t include participation in offline coding classes, which teachers are submitting over the weekend. CSEd week officially ends on Sunday at midnight.

The Partovis put together some estimates of the amount of computer science education that has happened in U.S. schools in the past 30 years. Their guess: a little under 5 million, including less than 1 million females (this would be hard to check, but it’s based on extrapolating from AP class enrollment to other levels).

Meanwhile, Hour of Code students were 73 percent from the U.S., and 51 percent female.

So in Code.org’s estimation, Hour of Code has reached twice as many U.S. students as have ever taken a computer science class, and five times as many U.S. females as have taken a computer science class. Ever.

Of course, it’s only an hour of code, so you don’t want to put too much weight on the extrapolation. But that’s the point: if more students get a taste of learning to code, more are likely to stick around.

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